Adaptive Metafilm With Scalable Phase‐Tunable Emissivity for Energy‐Efficient Thermal Management

ABSTRACT Efficient thermal management of enclosed systems through controlled manipulation of radiative cooling power represents a key functionality of adaptive composite metamaterials. Such materials enable precise regulation of heat emission under varying environmental conditions while maintaining scalability and durability. Here, we present an adaptive metafilm (AMF) that autonomously tunes its infrared (IR) emissivity near ambient temperature. The AMF is fabricated by embedding tungsten‐doped vanadium dioxide (W‐VO 2 ) and indium tin oxide (ITO) nanoparticles in a low‐density polyethylene (LDPE) matrix, followed by bottom‑side aluminum sputtering to form a reflective back layer. Through systematic optimization of filler loading and film thickness, an optimal configuration (5 wt.% W‐VO 2 | 1 wt.% ITO | 50 µm) was identified, providing maximal IR modulation by balancing absorption and multiple scattering. This design yields a transmittance tunability of up to 40.25% in the 9–11 µm wavelength range, enabling bidirectional switching between heat‐conserving and radiative‐cooling modes across ambient temperature transitions at 40°C. The flexible metafilm exhibits strong environmental stability, supported by a polyethylene‐based composite during repeated thermal cycling. Both optical and thermal evaluations demonstrate consistent thermoregulation without external power. This scalable, flexible AMF platform offers a practical route to net‐zero‐energy thermal regulation in buildings, enclosures, and mobile energy systems.